Biological Tissue Drying Before Supercritical CO2 Sterilization
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Solution Overview
Problem
Existing sterilization methods for dry biological tissue medical devices, such as ethylene oxide, pose health risks and require costly compliance measures, while supercritical carbon dioxide sterilization methods risk dehydrating and freezing the tissue when used with water.
Innovation Solution
A method involving chemical fixation, bioburden reduction, anti-calcification treatment, tissue purification, and drying followed by supercritical carbon dioxide sterilization to sterilize biological tissue without freezing or dehydrating it, using a sequence of treatments including glutaraldehyde, ethanol, and supercritical CO2.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ethylene oxide sterilization is used on dry biological tissue devices, then sterilization is achieved, but harmful carcinogenic residues remain on the device requiring expensive testing and compliance measures
Solution Approach 1:
The patent changes the chemical parameters of the sterilization agent from ethylene oxide to supercritical carbon dioxide, and adjusts the physical parameters (temperature 31-50°C, pressure 730-3000 psi) to achieve sterilization without harmful residues. This parameter transformation resolves the contradiction by maintaining sterilization effectiveness while eliminating carcinogenic contamination
Solution Approach 2:
The patent employs carbon dioxide as a sterilization agent that decomposes into harmless substances after use, unlike ethylene oxide that leaves persistent carcinogenic residues. The CO2 system requires no expensive residual testing and eliminates ongoing compliance costs, effectively replacing a problematic sterilization method with a cleaner alternative
2Reliability
If supercritical carbon dioxide sterilization is applied to wet biological tissue, then sterilization is achieved, but the tissue freezes and becomes brittle and irreversibly dehydrated
Solution Approach 1:
The patent applies a preliminary drying treatment to the biological tissue before subjecting it to supercritical carbon dioxide sterilization. This pre-drying step removes excess moisture that would otherwise cause freezing during the sterilization process, thereby preserving the tissue's mechanical properties while still achieving effective sterilization
Solution Approach 2:
The patent employs a preliminary anti-freezing measure by drying the tissue before sterilization. This counteracts the potential freezing effect that would occur during supercritical CO2 treatment, preventing the tissue from becoming brittle and maintaining its structural integrity throughout the sterilization process
3Reliability
If ethylene oxide sterilization is used, then sterilization is achieved, but expensive continuous emissions monitoring systems and stringent OSHA regulations compliance are required
Solution Approach 1:
The patent replaces ethylene oxide with carbon dioxide as the sterilization medium. CO2 is inherently safer, non-carcinogenic, and does not require expensive continuous emissions monitoring systems or stringent regulatory compliance. This substitution eliminates complex safety infrastructure while maintaining sterilization effectiveness
Solution Approach 2:
The patent uses carbon dioxide to create an inert sterilization environment that is inherently safe and does not require complex monitoring systems. The CO2 atmosphere is non-flammable, non-toxic at sterilization concentrations, and naturally dissipates without harmful residues, thereby eliminating the need for expensive compliance infrastructure required by ethylene oxide systems
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively sterilizes biological tissue without altering its crosslinking or mechanical properties, ensuring it remains suitable for bioprosthetic devices, with a six-log reduction in microbial contamination achieved under specific pressure, temperature, and cycle duration conditions.
Implementation Method 1
sterilizing the piece of biological tissue with supercritical carbon dioxide
Implementation Method 2
The step of chemical fixation of the piece of biological tissue comprises immersing the piece of biological tissue in an aqueous glutaraldehyde solution
Implementation Method 3
subjecting the piece of biological tissue to a tissue drying treatment
Data Source
AI summary
A method of sterilizing biological tissue such as soft mammalian tissue that can be used to make bioprosthetic devices is disclosed. The method comprises contacting biological tissue with a bioburden reduction mixture, contacting biological tissue with a tissue drying mixture, and thereafter sterilizing the dry tissue with supercritical carbon dioxide. Prior to sterilizing the biological tissue with supercritical carbon dioxide, the biological tissue is placed under vacuum and, in some embodiments, is treated with a vaporized microbicide. Bioprosthetic devices made using the methods disclosed herein include bioprosthetic heart valves, biological tissue derived vascular grafts or vessels, and surgical tissue patches.